1. Field
One embodiment of the present invention relates to a magnetic disk drive comprising two pole cores.
2. Description of the Related Art
It is demanded for a perpendicular magnetic recording head to reduce the physical width of the main pole responding to high track density. If the physical width of the main pole is reduced, however, a steep field gradient in the cross-track direction cannot be achieved due to fringe characteristics of the write field generated from the main pole in the cross-track direction, making it difficult to maintain recording ability.
Conventionally, it has been proposed that a side shield be formed in order to improve the fringe characteristics of the main pole (see, for example, IEEE TRANSACTION ON MAGNETICS, pp. 2914-2919, Vol. 41, No. 10, October 2005). Once a magnetic recording head having a side shield has been manufactured, however, the fringe characteristics of the main pole can only be adjusted with a write current supplied to the main-pole coil. Thus, if the physical width, bevel angle or flare angle of the main pole is deviated from a design value by process dispersion, degraded fringe characteristics can hardly be corrected.
In view of this, it may be considered that a first coil is arranged for a first pole core comprising the main pole and a second coil is arranged for a second pole core (subsidiary pole), tip ends of which are arranged on both sides of the main pole in the track-width direction so as to control current supplied to the first coil and the current supplied to the second coil independently, thereby to improve the fringe characteristics of the main pole.
In the recording system that uses two pole cores that are magnetically independent of each other as described above, the currents supplied to the coils independently wound around the two pole cores may produce a phase difference by which a write field distribution may be distorted and further magnetization patterns recorded on the magnetic disk may have write distortion. If the write distortion is produced, the waveform of read output is also distorted, bringing about degradation in the bit error rate.